The invention relates to an electro-optical distance measuring system for large measurement ranges with parallel spaced arrangement of the optical transmitting and receiving axes, in para-axial arrangement, as an easy-to-use distance measuring device.
One such electro-optical distance measuring system, as described in U.S. Pat. No. 4,403,857, for example, features in addition to the computing and input/output unit, a phase and echo time measurement and a reference photo diode, particularly a beam source with transmitting optics and a separate beam receiver with receiving optics, whose optical axes are each oriented parallel to the measuring beam. The primary light beam leaving the beam source is, after collimating in a collimating lens, split into a measurement light beam and a reference light beam that impinges on the reference photo diode. Conventionally, the beam source has transmitting optics and a beam receiver with receiving optics each as a structural unit. The measurement range limited by the dynamics range and the effective aperture of the beam receiver is, in distance measuring systems of such simple design principle, too small.
According to DE19513823, in an electro-optical coaxial distance measuring system, the beam source designed as a laser diode and the beam receiver are each electrically conducting fastened directly to a common, rigid circuit board with other electronic components and oriented vertically to each other. Additionally, upstream of the transmitting optics, reference light beam output coupling of the primary light beam is at a reference photodiode. There is no para-axial arrangement of the optical transmitting and receiving axis, whereby additional beam deflection means such as deflection mirrors are required.
According to DE19855296, a large-area photodiode not requiring adjustment is used as the beam receiver. In use, large-area photodiodes enable only a small measurement range due to interference effects such as external light, homogeneity defects on the active detector surface, dark current and interference reflections from the local environment and on smaller limited measurement frequencies, e.g. 500 MHz. In addition, they have a comparatively high measurement error and require long measuring times.
According to DE 19860464, a manual laser distance measuring device for the large measuring ranges of from 0.30 m to 30 m common in the construction trade features in the focal point of the receiving optics a small-area photodiode for minimizing interference effects and modified receiving optics with an addition secondary focal point offset at an angle for the image, which is offset by the para-axial arrangement, of a measurement object situated in the near range. Essential to this solution is that the modified receiving optics features precisely two focal points on the image side, which arise in that the receiving lens consists of a primary lens region and a secondary lens region, wherein the secondary lens region runs, extended over the entire diameter of the receiving lens, vertical to the transmitting axis and has a trapezoidal shape, which becomes narrower towards the transmitting axis. The two lens regions are dimensioned so that over the entire desired distance range a reflex signal lying within its sensitivity range is received by the beam receiver.
The purpose of a highly sensitive distance measuring device is minimization of the interference effects limiting the measurement range, in particular those interference effects that are produced by detected foreign light. For reducing impingement of foreign light either small detector surfaces and/or large focal distances of the receiving optics can be used. When such an arrangement is used, the ratio of detector diameter to focal distance has a decisive role. The smaller the ratio, the less interfering foreign light is detected. In non-circular area active detector surfaces or in arrangements with a plurality of detector surfaces one refers to diameter in the following, whereby a circular area of equivalent detector diameter is meant. A small ratio of equivalent detector diameter to focal distance of the receiving optics makes the configuration and particularly the photodiode relative to the receiving optics and the measurement light beam, needful of adjustment. Such adjustment, which usually, for example, according to EP701702, is made possible by mechanically adjustable beam adjustment systems in the measurement path such as a light guide fiber, which represents potential sources of error in the rough construction industry.
During the adjustment procedure, the laser measurement device and conventional adjustment auxiliary means is adjusted, in the presence of an activated measurement light beam, to the optimal beam path. For the purpose of simplified description, reference will be made in the following to a small-area photodiode, wherein the small ratio of equivalent detector diameter to focal distance to the receiver optics is meant. Measures for signal extension for the lower distance measuring range are required since configurations with a small ratio of detector diameter to focal distance tend towards a strong lateral offset of the imaged light spot so that in short distances, under certain circumstances, no light reaches the photosensitive surface.
The measures are either the use of additional elements in the receiver beam path, which as in the device of DE 19860464, generate an additional secondary focal point or deflection elements, and as in the device of EP 701702, which guide the light from the near range to the active detector surface. Likewise, moveable active deflector surfaces, as in the device of EP 701702, can be used. Another measure is the use of at least one second active detector surface, which especially detects light from the near range. A slit-like active detector surface is also possible, wherein decreasing distance parts of the imaged measurement light beam run along the slit. All measures described are characterized in the description as measures for signal extension for the lower distance measurement range.
The object of the invention is to provide a robust adjustable, para-axial distance measuring device for large measurement ranges. A further object is that the adjustment procedure should require the shortest possible time and should be easy to automate. Additional beam deflection systems or beam adjustment systems such as deflecting mirrors and mechanical devices for tilting and offsetting should be eliminated. Such an arrangement results in a reduction of costs and in increased reliability of the distance measuring device because of the reduced component requirement.
This object is achieved, in accordance with the invention, by an electro-optical distance measuring system for large measuring ranges having a para-axial arrangement of a beam source with transmitting optics and a beam receiver, designed as at least one small-area photodiode, with receiving optics, which contains processing for signal extension for the lower distance measuring range. The beam source, the transmitting optics, the receiving optics and the beam receiver are each oriented parallel to the measurement light beam. The measurement light beam reaches directly; that is, without beam deflection devices or beam adjustment devices, through a protective window, through the transmitting optics to the measurement object and to the receiving optics. The beam source and the small-area photodiode are rigidly connected with each other by at least one intrinsically rigid connected circuit board. At least the small-area photodiode electrically conducts and temporarily adjusts to the position using its electrical contacts and, optionally, using its housing fixed directly to the adjusted position on the circuit board.
A robust para-axial distance measuring system is realized as result and, temporarily during the adjustment process, is adjustable in the position of the small-area photodiode with respect to the receiving optics, for example, by an enlarged adjustment gap between the contacts of the photodiode and the circuit board and/or enlarged contact surfaces on the circuit board.
Advantageously, the beam source electrically conducts and temporarily adjusts to the position using its electrical contacts and, optionally, using its housing fixed directly in the adjusted position on the circuit board, whereby temporarily during the adjusting process the position of the beam source is adjustable relative to the transmitting optics, which preferably are designed as collimating optics.
Advantageously, a beam source module, which connects the beam source rigidly to the transmitting optics, is fixed with the electrical contacts of the beam sources and, optionally, using the housing of the beam source, on a circuit board shared with the small-area photodiode, wherein the beam source module itself is pre-adjustable.
Advantageously, the laser distance measuring device features a rigid optics carrier, on which both the transmitting optics or the beam source module and the receiving optics are fixed, whereby a para-axial arrangement of the transmitting optics and the receiving optics is realizable in a technologically simple fashion.
Advantageously, the at least one circuit board is rigidly connected with the optics carrier using fastening means such as screws, rivets or adhesive, whereby a robust, rigid arrangement of the beam source with the associated transmitting optics and/or the beam receiver with the associated receiving optics is established by the optics carrier and the circuit board.
Advantageously, the beam source and the small-area photodiode and a circuit board, which are connected with the rigid optics carrier, are fixed directly using their respective electrical contacts and, optionally, using their respective housings, in a respective adjusted position, whereby the respective transmitting module and the receiving module having the additionally required electronic components can be prefabricated separately on separate circuit boards.
Advantageously, the beam source fixed directly on the circuit board, in position in the direction of the beam, using the electrical contacts and, optionally, using the housing is friction locking introduced into the rigid optics carrier and fixed on the circuit board shared with the small-area photodiode, whereby during the adjustment process with the activated beam source, the position of the beam source is temporarily adjustable with respect to the transmitting optics, in the direction of its optical axis.
Advantageously, the beam source module is connected rigidly with the rigid optics carrier and bonded on the circuit board sing the electrical contacts of the beam source, wherein a pre-adjusted beam source module can be used.
Advantageously, the focal distance of the receiving optics is less than 40 mm; also advantageously, the focal distance of the receiving optics is less than 25 mm, whereby, mediated by the strong refractory power, even angularity offset portions of the measurement beam reflected in the near range reach the small-area photodiode. In addition, the receiving optics can be combined with a color filter corresponding to the wavelength of the measurement light beam.
Advantageously, the ratio of the equivalent detector diameter to the focal distance of the receiving optics is less than 0.005, preferably less than 0.001, whereby a high resistance to interference, particularly relative to foreign light and parasitic reflection from the near range or local environment, is achieved.
Advantageously, the small-area photodiode has an active surface in the diameter of less than 100 xcexcm, preferably less than 30 xcexcm, whereby a high degree of resistance to interference, in particular, relative to foreign light, parasitic reflection from the near range or local environment, homogeneity defects on the photosensitive surface and dark current, is achieved.
Advantageously, the small-area photodiode is configured as a large-area photodiode with an associated mask, which is advantageously configured as an opaque applied layer shielding the active surface, having at least one aperture opening, whereby a defined dimension and positioning of the active surface of the small-area photodiode can be easily established.
Advantageously, other active surfaces, by additional aperture openings of the mask or additional small-area photodiodes are arranged para-axially offset to the first active surface, whereby angularity offset portions of the measurement light beam reflected in the near range with defined intensity reach at least one active surface.
Advantageously, the small-surface photodiode or the aperture opening of the mask is delimited slitlike in one dimension such that with decreasing distance, parts of the imaged measurement light beam run along the longitudinal active surface, whereby angularity offset portions of the measurement light beam reflected in the near range with defined intensity reach the active surface.
Advantageously, the small-area photodiode is configured as an SMD photodiode, whereby miniaturization and cost effectiveness are favored.
Advantageously, a reference photodiode is provided, on which a reference light beam deflected from a primary light beam impinges, whereby an internal calibration of distance measuring is possible.
Advantageously, a reflection means is arranged between the beam source and the transmitting optics for providing reference light beam output coupling and which reflects or deflects a portion of the primary beam as a reference light beam to the photodiode or to a reference photodiode, whereby local homogeneity defects in the reference light beam can be avoided, which, caused by the laws of Fourier optics, are possible in a reference light beam output coupling downstream of the transmitting optics.
Advantageously, the reflection means is an exclusively diffusely reflecting diffusion body arranged in a radial marginal zone of the divergent primary beam exiting from the beam source, said diffusion body being designed as a diffusion contour of the optics carrier projecting into the diverging primary beam or as a diffusion spot on the diffusion mounting around the transmitting optics, which is technically simple.
In the associated adjustment process in the combined distance measuring system combined with the usual optical adjustment aids, for example a camera arranged at optical infinity, with activated measurement light beam at least the small-area photodiode, preferably by a manipulator controlled by a feedback loop at an automatically adjusted adjustment target value, is in a first step shifted relative to the circuit board so that a measurement light beam reflected or back-scattered into infinity impinges on a predefined zone of the small-area photodiode and, in a second step, the small-area photodiode is fixed using its electrical contacts electrically conducting directly, e.g. using soft solder or conducting adhesive, to an adjusted position on the circuit board. By doing this, the distance measuring system can be automatically adjusted as a unit.
The advantage of this adjustment method is that only one component must be adjusted, whereby adjustment without tilting is sufficient. In connection with the adjustment, only one stable, position-holding mechanical connection is required. The process is thus easily automated. The adjustment of the small-area photodiode can be done both manually and automatically using a manipulator with a robot and image processing.
Advantageously, the beam source is shifted, in the associated adjustment process with an activated measurement light beam, into a predefined first collimating adjustment step relative to the circuit board so that the measurement light beam is focussed in infinity and in a predefined collimating adjustment step the beam source is electrically conductive directly fixed to an adjusted position on the circuit board, using its electrical contacts, or using soft solder or conductive adhesive. As a result, the collimator can be automatically separately adjusted. Preferably, the beam source is shifted by using a manipulator controlled automatically to an adjustment target value by a feedback loop.